The present invention relates to a fluid pressure boosting device, which boosts operating force exerted on an operating means with working fluid pressure into predetermined magnitude to output boosted force and, more particularly, to a fluid pressure boosting device with a so-called jumping characteristic.
For example, fluid pressure boosting device is employed in a brake fluid pressure boosting device of a type utilized in brake systems of automotive vehicles. Such a brake fluid pressure boosting device is for boosting pedaling force on a brake pedal into predetermined magnitude to output. The output of the brake fluid pressure boosting device actuate a master cylinder so that the master cylinder develops master cylinder pressure corresponding to the output of the brake fluid pressure boosting device. The master cylinder pressure is supplied to wheel cylinders, thereby actuating brakes.
Among conventional brake fluid pressure boosting devices, a brake fluid pressure boosting device of a center-valve type with a so-called jumping characteristic is known in which a control valve is located in a power piston. According to the jumping characteristics, as shown in FIG. 3, little or none output is produced until loss stroke in the brake system is cancelled so that substantial brake pressure is attained after, while large output is produced when substantial brake pressure is attained after loss stroke in the brake system is cancelled. Because of the jumping characteristic, the braking pressure boosting device can output braking pressure well corresponding to the input as compared to a device without jumping characteristic as shown by a dotted line of FIG. 3.
As an example of conventional brake fluid pressure boosting devices having the aforementioned jumping characteristic is disclosed in Japanese Unexamined Patent Publication No. 2000-177576.
FIG. 4 is a sectional view showing a brake fluid pressure boosting device and a tandem-type master cylinder disclosed in the above publication. The master cylinder is actuated by output of the brake fluid pressure boosting device. Detail explanation of components and actions of the brake fluid pressure boosting device and the master cylinder will be omitted because these should be understood upon a reading of the publication. The components and actions will be just simply explained.
When any braking action is not taken as shown in FIG. 4, in the brake fluid pressure boosting device 1 and the master cylinder 2, a brake pedal (not shown) is not depressed so that an input shaft 3 connected to the brake pedal does not travel and a control valve 4 is thus in its inoperative state as shown in FIG. 4. That is, a valve ball 5 of the control valve 4 is seated on a first valve seat 7 fixed to a power piston 6 and is spaced apart from a second valve seat 8 disposed on an end of a cylindrical member 8a connected to the input shaft 3 integrally. Therefore, a power chamber 9, which is always in communication with a second-valve-seat-side portion of the cylindrical member 8a, communicates with a booster reservoir (not shown) through a space between the valve ball 5 and the second valve seat 8, an axial hole 10 formed in the cylindrical member 8a, an axial hole 11 and a radial hole 12 formed in the input shaft 3, a radial hole 14 formed in a plug 13, an axial hole 16 formed in a housing 15, and a discharge port 17. Hydraulic fluid introduced from a fluid pressure source (not shown) through an input port 18 is not supplied to the power chamber 9. Therefore, the power piston 6 is not actuated and the brake fluid pressure boosting device 1 outputs nothing.
The right end 19a of a reaction piston 19 which is slidably fitted around the input shaft 3 is spaced apart from a step 3a of the input shaft 3. In addition, a flange (stopping portion) 20a of a cylindrical stopper member 20 connected to the input shaft 3 is in contact with an end 13b of a cylindrical projection 13a of the plug 13 and is spaced apart from a stopper 19c of a first flange 19b of the reaction piston 19. That is, the flange 20a of the cylindrical stopper member 20 is in a position advanced relative to the stopper 19c. 
The master cylinder 2 is also not operated. In this state, a radial hole 22 formed in a primary piston 21 is positioned behind a cup seal 23 so that a primary chamber 24 communicates with a master-cylinder reservoir 27 through the radial hole 22 and holes 25, 26. Further, a radial hole 29 of a secondary piston 28 is in a position behind a cup seal 30 so that the secondary chamber 31 communicates with the master-cylinder reservoir 27 through radial holes 29 and passages 32, 33. Therefore, no master cylinder pressure is developed in the primary chamber 24 and the secondary chamber 31.
Upon depression of the brake pedal for braking operation, the input shaft 3, the cylindrical stopper member 20, and the cylindrical member 8a advance so that the valve ball 5 is seated on the second valve seat 8 and is spaced apart from the first valve seat 7, thereby switching the control valve 4. Therefore, the power chamber 9 is isolated from the booster reservoir, which is always in communication with the axial hole 10 of the cylindrical member 8a, and communicates with the input port 18, whereby hydraulic fluid is introduced into the power chamber 9 from the fluid pressure source. By the hydraulic fluid introduced into the power chamber 9, the power piston 6 advances so that the brake fluid pressure boosting device 1 outputs. Then, the primary piston 21 advances such that the radial hole 22 passes the cup seal 23, thereby isolating the primary chamber 24 from the master-cylinder reservoir 27. As a result, master cylinder pressure is developed in the primary chamber 24.
At the same time, the hydraulic fluid in the power chamber 9 is introduced into both wheel cylinders of one circuit of the brake system through a hole 34 formed in the housing 15. Because of the master cylinder pressure developed in the primary chamber 24, the secondary piston 28 advances such that its radial hole 29 passes the cup seal 30, thereby isolating the secondary chamber 31 from the master-cylinder reservoir 27. As a result, master cylinder pressure is developed in the secondary chamber 31 too. The master cylinder pressure developed in the secondary chamber 31 is introduced into both wheel cylinders of the other circuit of the brake system from a secondary output port 35.
As mentioned above, the inner pressure of the power chamber 9, and the respective master cylinder pressures of the primary chamber 24 and the secondary chamber 31 are equal to each other so that hydraulic fluid at the same fluid pressure is supplied to the respective wheel cylinders. That is, braking pressures at the two circuits of the brake system are equal to each other. The hydraulic fluid in the power chamber 9 is also introduced into a chamber 37 through an axial hole 36. By the fluid pressure in the chamber 37, a valve member 38 supporting the valve ball 5 is biased in a direction against the input of the input shaft 3.
Because of the fluid pressure in the power chamber 9, the reaction piston 19 is shifted to the right relative to the power piston 6 and the input shaft 3 against the spring force of the spring 39. Since loss strokes exist in the respective wheel cylinders, however, no braking force is substantially produced by the wheel cylinders at an initial operational stage. In this initial operational stage, the rear end (the right end in FIG. 4) 19a of the reaction piston 19 moves to such a position before the step 3a of the input shaft 3. Therefore, the rear end 19a of the reaction piston 19 does not come in contact with the step 3a of the input shaft 3 so that no force is exerted on the input shaft 3 from the reaction piston 19. Therefore, exerted on the input shaft 3 is a small force which is received by relatively small effective pressure receiving areas of the cylindrical stopper member 20 and the cylindrical member 8a located at the end of the input shaft 3. This small force is transmitted as a reaction force to a driver.
As the reaction force on the input shaft 3 becomes equal to the input on the input shaft 3, the valve ball 5 is seated on both of the first valve seat 7 and the second valve seat 8 so that the power chamber 9 is isolated from both of the fluid pressure source and the booster reservoir. As the input of the input shaft 3 further increases, the valve ball 5 is again spaced apart from the first valve seat 7 so that the hydraulic fluid from the fluid pressure source is supplied in the power chamber 9 to further increase the fluid pressure in the power chamber 9. After that, the seating and separating motion of the valve ball 5 relative to the first valve seat 7 is repeated so as to successively increase the fluid pressure in the power chamber 9 at a predetermined boosting rate according to the increase in the input of the input shaft 3.
During the loss strokes of the respective wheel cylinders, since the rear end 19a of the reaction piston 19 is not in contact with the step 3a of the input shaft 3, the effective pressure receiving area of the input shaft 3 on which the fluid pressure in the power chamber 9 acts is small so that the boosting rate is high. Therefore, the output of the brake fluid pressure boosting device 1 is significantly increased at this high boosting rate relative to the input of the input shaft 3, that is, the brake fluid pressure boosting device 1 performs so-called jumping action.
As the power piston 6 further advances by the further increase in the fluid pressure in the power chamber 9 to cancel the loss strokes of the wheel cylinders, the respective wheel cylinders substantially develop braking forces so that the brakes of the two circuits of the brake system are substantially operated. In this state, the rear end 19a of the reaction piston 19 is in contact with the step 3a of the input shaft 3 because of the increased fluid pressure in the power chamber 9 and, because of biasing force produced by the fluid pressure in the power chamber 9, the reaction piston 19 applies force to the input shaft 3 against the input of the input shaft 3. Therefore, the reaction force acting on the input shaft 3 is increased and the output of the brake fluid pressure boosting device 1 is increased at an boosting rate, lower than that during the loss strokes, relative to the input of the input shat 3. That is, the jumping action is ended.
After that, since the reaction force is increased, the brake fluid pressure boosting device 1 boosts the input of the input shaft 3 at a normal and relatively low increasing ratio and the fluid pressure in the power chamber 9 becomes fluid pressure corresponding to this boosting rate. The hydraulic fluid of the power chamber 9 is supplied to the wheel cylinders of the one circuit, while the master cylinder 2 develops master cylinder pressure by the output of the brake fluid pressure boosting device 1 and the master cylinder pressure developed in the secondary chamber 31 is supplied to the wheel cylinders of the other circuit. Accordingly, the respective wheel cylinders of the two circuits generate large braking force relative to the input of the input shaft 3 so that the brakes are operated by this braking force.
As the brake pedal is released to cancel the operation of the brakes, the input shaft 3, the cylindrical stopper member 20, and the cylindrical member 8a move rearward to the right. As mentioned above, the second valve seat 8 of the control valve 4 is spaced apart from the valve ball 5 so that the power chamber 9 communicates with the axial hole 10, i.e. the booster reservoir to discharge the hydraulic fluid out of the power chamber 9 to the booster reservoir.
Because of the discharge of the hydraulic fluid out of the power chamber 9, the hydraulic fluid in the wheel cylinders of the one circuit are also rapidly discharged to the booster reservoir through the power chamber 9. In addition, the primary piston 21, the secondary piston 28, and the power piston 6 are rapidly moved rearward by the spring force of the primary return spring 40 and the secondary return spring 41. By the rearward movement of the primary piston 21 and the secondary piston 28, the radial holes 29 and 22 pass the cup seals 30 and 23 to be positioned behind the cup seals 30 and 23, respectively so that both the primary chamber 24 and the secondary chamber 31 communicate with the master-cylinder reservoir 27. Therefore, hydraulic fluid in the wheel cylinders of the other circuit is also discharged to the master cylinder reservoir 27 through the secondary chamber 31. Therefore, the operation of brakes of the both circuits is rapidly cancelled.
As the fluid pressure in the power chamber 9 is decreased to a predetermined pressure, the reaction piston 19 moves forward relative to the power piston 6 and the input shaft 3 by the spring force of the spring 39, whereby the reaction piston 19 comes in contact with a flange of a valve seat member 7a composing the first valve seat 7 provided on the power piston 6 and the rear end 19a of the reaction piston 19 is spaced apart from the step 3a of the input shaft 3.
As the rear end of the power piston 6 comes in contact with the plug 13 as shown in FIG. 4, the rearward movement of the power piston 6 is stopped, so the power piston 6 is in its inoperative position. Accordingly, the rearward movement of the primary piston 21 and the secondary piston 28 of the master cylinder 2 is also stopped, so the primary piston 21 and the secondary piston 28 are in their inoperative positions. In this manner, the operation of the brakes are rapidly cancelled.
In case that no hydraulic fluid is supplied to the power chamber 9 from the fluid pressure source during the braking operation due to failure of fluid pressure source, as the input piston 8 is moved forward by depression of the brake pedal, the cylindrical member 8a comes in contact with the valve ball 5 similarly to the aforementioned normal case and presses the valve member 38 via the valve ball 5. Then, the stopping portion 20a of the cylindrical stopper member 20 comes in contact with the flange of the valve seat member 7a of the first valve seat 7. As a result, the input shaft 3 directly presses the primary piston 21 via the cylindrical stopper member 20, the valve seat member 7a, the power piston 6, and an adjusting member 42, thereby moving the primary piston 21 forward. Therefore, the radial hole 22 advances to the front side of the cup seal 23 so that master cylinder pressure is developed in the primary chamber 24 similarly to the aforementioned normal case. By the master cylinder pressure in the primary chamber 24, the secondary piston 28 is moved forward and the radial hole 29 advances to the front side of the cup seal 30 so that the master cylinder pressure is developed in the secondary chamber 31. The master cylinder pressures in the primary chamber 24 and the secondary chamber 31 are supplied to the wheel cylinders of the two circuits of the brake system through the primary output port 43 and the secondary output port 35, respectively, thereby operating the brakes of the two circuits of the brake system. In this manner, even in case of the fluid pressure source failure i.e. pump failure, the brakes of the two circuits of the brake system can be securely operated. In this case, the characteristic of the brake fluid pressure boosting device is indicated by a solid straight line without any boost in FIG. 3.
The aforementioned conventional brake fluid pressure boosting device 1 with the jumping characteristic by the reaction piston 19 in which the control valve 4 having the valve ball 5 is arranged in the power piston 6 however has problems that the structure for attaining the jumping characteristic is complex because special parts for attaining the jumping characteristic such as the reaction piston 19 slidably disposed to the input shaft 3 and the spring 39 for biasing the reaction piston 19 should be employed, and that the cost is high because of these special parts.
To solve these problems, instead of the reaction piston 19 and the spring 39, a reaction mechanism composed of a reaction disk made of an elastic material such as rubber which is conventionally known to be used in a vacuum boosting device may be employed in this brake fluid pressure boosting device 1. However, for achieving this arrangement, the input shaft 3 should be designed to penetrate the valve ball 5 and rigidity for transmitting the reaction force to the input shaft 3 is also required. That is, it is difficult to employ the reaction mechanism composed of the reaction disk.
There is another problem that the structure for the control valve 4 is complex. Since fluid pressure in the power chamber 9 acts on the valve ball 5 of the control valve 4 during operation, hydraulic fluid of the power chamber 9 is introduced into the chamber 37 so as to make the fluid pressure of the chamber 37 to act on the valve member 38 in order to prevent the valve ball 5 from being spaced apart from the second valve seat 8, thus making the structure for the control valve 4 complex.
There is further another problem that the passage for discharging hydraulic fluid out of the power chamber 9 is complex because the holes 10, 11, 12, 14, and 16 composing the passage for discharging hydraulic fluid are formed in the cylindrical member 8a, the input shaft 3, the plug 13, and the housing 15, respectively.
It is an object of the present invention to provide a fluid pressure boosting device of a center valve type of which the structure for attaining the jumping characteristic and the structure of passage for discharging hydraulic fluid are simple.
To achieve the aforementioned object, the present invention provides a fluid pressure boosting device, for boosting an input by fluid pressure to output the boosted pressure, comprising at least a power chamber to which hydraulic fluid from a fluid pressure source is supplied during operation, a power piston which is actuated by fluid pressure of said power chamber to output, a control valve which is arranged inside said power piston to control the supply and discharge of the hydraulic fluid of said power chamber, and an input shaft for operating said control valve according to the input, said fluid pressure boosting device being characterized in that said control valve comprises a supply valve which stops the supply of hydraulic fluid from said fluid pressure source to said power chamber in the inoperative state and allows the supply of hydraulic fluid from said fluid pressure source to said power chamber according to said input in the operative state, and a discharge valve which allows the discharge of hydraulic fluid of said power chamber in the inoperative state and stops the discharge of hydraulic fluid of said power chamber in the operative state, wherein said supply valve has an annular poppet valve element supported by a cylindrical supply valve member which is slidably arranged in said power piston and a supply valve seat which is arranged in said power piston and in which said poppet valve element can be seated, and said discharge valve has an annular poppet valve element supported by a cylindrical discharge valve member disposed integrally with said supply valve member and a discharge valve seat which is disposed to move together with said input shaft and to which the latter poppet valve element can be seated, and that said input shaft extends to penetrate said supply valve and said discharge valve in the axial direction and is arranged such that, in the inoperative state, an end of said input shaft confronts the reaction disk arranged in an output-side member with a predetermined space therebetween and, in the operative state and when producing a predetermined output, the end of said input shaft comes in contact with said reaction disk so that a reaction force is transmitted from said reaction disk to said input shaft.
The present invention is characterized in that said output-side member is said power piston or a piston of a master cylinder which is actuated by said power piston.
The present invention is characterized in that a passage for discharging hydraulic fluid of said power chamber is composed of annular passages which are formed between an outer surface of said input shaft and an inner surface of said supply valve member, between the outer surface of said input shaft and an inner surface of said discharge valve member, and between the outer surface of said input shaft and an inner surface of the poppet valve element supported by said discharge valve member.
According to the fluid pressure boosting device of the present invention having the aforementioned structure, a control valve is composed of a two-element-two-seat control valve of a poppet valve type, the front end of an input shaft penetrating the control valve is arranged to confront a reaction disk with a predetermined space therebetween in the inoperative state, the reaction disk being disposed in an output-side member, and to come in contact with the reaction disk in the operative state, thereby ensuring well fluid tightness (sealing property) and shortening the loss strokes. In addition, the reaction disk which is cheap is used for attaining the jumping characteristic, thereby simplifying the structure for attaining the jumping characteristic, and manufacturing the fluid pressure boosting device at a low cost.
In particular, according to the present invention, the discharging passage for discharging hydraulic fluid of a power chamber is composed of annular passages which are formed between the outer surface of an input shaft and the inner surface of a supply valve member, between the outer surface of the input shaft and the inner surface of a discharge valve member, and between the outer surface of said input shaft and the inner surface of the poppet valve element supported by the discharge valve member. Since the annular passages are normally formed at the discharge side, i.e. the side of a reservoir to which hydraulic fluid of the power chamber is discharged, the discharging passage directly extends to the reservoir side. Therefore, unlike the conventional example, the discharging passage is not required to extend toward the input side, thereby further securely simplifying the structure of the discharging passage.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.